Brickwork:
Historic Development,Decay, Conservation and Repair

Gerard
Lynch

Previously
considered to be an inferior material to stone, brick construction was
rarely used in Britain until the close of the Middle Ages. Gerard Lynch
looks at its historical development over the last 600 years and its conservation
and repair.

TUDOR
BRICKWORK 1485-1603

The
popularity of the material can be traced to the revival of brick-making
in eastern England in the late 13th and early 14th centuries. This was
a direct result of lack of local stone, an increasing shortage of good
timber, and the influence of Europe where brickwork was used extensively.

By
the Tudor period the brick-makers and bricklayers had emerged as separate
craftsmen well able to rival the masons. From unsophisticated early work,
brick building entered its heyday, rivalling stone in its popularity as
a structural material.

Bricks
were generally made on site in wood, heather or turf fired clamps by itinerant
workers. Not only were standard bricks produced but also many in extravagant
and elaborate shapes, epitomised by those that formed the spiral twisted
chimney stacks for which the period is renown.

The
Tudors further patterned their brickwork by inserting headers of over
burnt or vitrified bricks into the walling. These dark surfaces ranging
from deep purple to slate in colour, were laid carefully in quarter brick
offsets in mainly English bond or English cross-bond, to
form a diaper or chequered pattern within the predominantly red brickwork.

Tudor
bricks were irregular in size and shape and therefore thick (15-25mm)
mortar joints were necessary to even these out. The slow setting mortar
was of matured non-hydraulic lime (often containing particles of the fuel
used in its production), and coarse sand in a ratio varying from 1:2-1:5, the joints being finished flush from the laying trowel.

With
the building of Hampton Court Palace, we have not only the seal of royal
approval, but a monument to the achievement of brick in this period.

THE
GEORGIAN PERIOD 1714-1830

The
late 17th and early 18th centuries were a high point in the use of brick.
Their manufacture was much improved, with blended clay, better moulding
and more even firing which lead to greater consistency in shape and size.
The colours of bricks changed in popularity from red, purple or grey bricks
fashionable in the late 17th century until 1730, when brownish or pinkish
grey stocks replaced the hot colours. These were followed in the mid 18th
century by grey stocks, and, by 1800, the production of yellow
marl or malm London stocks, which were closer to the stone colour
desired for a classical facade.

Brickwork
was generally of a very high standard, in mainly Flemish bond although header bond was also popular in the early 18th century.

Pointing
was executed to a similar standard. As well as giving more protection
to the weaker bedding mortar, fine detailing also helped to minimise the
visual impact of the joints so that the classical details could be displayed
more clearly. 'Tuck' pointing was the ultimate development in this
quest.

A
more expensive solution was to use 'gauged' brickwork popularised
by Wren using a facade of fine, colour-matched bricks cut and rubbed to
exact units, and laid in thin lime putty joints. However after 1730 this
was considered too expensive and was reserved for window arches, aprons
and other ornamentation only.

VICTORIAN
BRICKWORK 1830-1914

This
was a period of revivalism in domestic architecture and industrial building.
The former seeking a return to 'medievalism' and other exotic building
forms as a relief from the unspirituality of the Machine Age. The latter,
for the infrastructure of factories, warehouses, railway bridges and so
on, all largely met through the cheap use of bricks.

During
this period, a greater number of bricks were made and laid than during
all the previous periods. Brick manufacturing methods had improved in
all respects including quality accuracy, regularity and in range of colours
available. From the mid 18th century onwards the manufacturing process,
like many others, was becoming mechanised. This enabled deeper clays to
be used for pressing into dense bricks for use on civil engineering works.

With
improvements in travel and communications, bricks could be transported
over wide areas which removed the traditional local variations.

Improvements
in the production of mortar also occurred during the late 18th century
through the use of washed and graded aggregates, often with colouring.
Also, the development of natural cements including Roman cement and other
hydraulic limes, which set quicker and stronger, were vital to the speed
of construction that the Industrial Age demanded. Portland Cement appeared
in the mid 19th century.

Joints
reduced to 0.3 inches (8mm) due to the accuracy of the machine pressed
bricks and continued to be finished in various profiles. These were popular
from the 17th century although the new 'weather-struck' and 'cut' style of joint became particularly popular.

A
variety of face bonds were now used although, in the main, Flemish bond
predominated domestically, whilst English bond was favoured industrially.

In
all matters of brickwork, the Victorian desire for enrichment was readily
achieved by the use of often garish polychromatic work, and the lavishing
of ornamentation by detailing mass produced purpose moulded 'specials' or by gauged brickwork.

Carved gauged brickwork to a doorway in Farnham c1717

DECAY,
CONSERVATION AND REPAIR

Before
considering the most appropriate method of repairing brickwork, correct
diagnosis of the cause of failure is vital.

Manufacturing
defects in bricks can be the result of under firing or impurities in the
clay used. These bricks decay more rapidly than better burnt bricks, especially
with frost action. They can also act as a point of entry for moisture,
which in turn will affect the whole wall, leaving it open to damage from
frost and chemical action. Free standing walls, parapets and retaining
walls are particularly vulnerable, and some judicious replacement may
be necessary.

Poor
detailing can also contribute to failure through construction defects
such as:

Decayed
bond timbers, joists, timber lintels, plates or bearers which have
been embedded or built in to the masonry.

The
expansion of rust on corroding iron and steel structural members,
wall ties or reinforcement embedded in the brickwork.

Failure
of arches and lintels from inadequate bearings, or abutments.

Poor
bonding and inadequate or even non-existent tying-in of brickwork.
This can be due to a habit in the 18th and 19th centuries of 'snapping' headers leading to a wall of two skins, instead of one mass. Alternatively
failure can occur at the junctions between walls, particularly where
front and rear walls are insufficiently tied to the cross walls.

'Corbelling' (over projecting brickwork) and oversailing are especially prone
to being insufficiently tailed-in to the main walling. They are also
susceptible to water penetration due to inadequate, or non-existent
protective weathering.

Sulphate
attack occurs when water is present with cement based mortars, producing
slow steady expansion of sulphate crystals within the mortar or the
bricks as the water evaporates. It can result in damage and even failure
of the masonry. This is particularly common in unlined chimney stacks,
where sulphates have been introduced by the burning of sulphur-rich
fossil fuels. Where chimneys have been designed without bends, allowing
rain straight down the flue, damp may appear on the chimney breast
with a possible resultant salt problem. This can especially occur
when the air is humid, or where the fireplace has been sealed without
proper ventilation.

INDUCED
DECAYRemedial
work to historic brickwork must be carefully selected after expert analysis
and should always be kept to an absolute minimum.

Consolidants
should only be applied to decaying brickwork as a last resort. Although
predictably effective on soft porous bricks their use is still in
its infancy, and the long term affects of new techniques is less certain.
The consolidated brick face may behave in a different manner from
the base through thermal movement, resulting in eventual separation.

Sealants
may induce similar problems. By sealing the surface they may inhibit
or reduce surface evaporation leading to a build up of moisture. This
can result in concentrating evaporation in other areas where crystallisation
and frost damage may be exacerbated. Sealants should only be used
in localised areas to prevent problems such as the staining which
occurs from water run-off from limestone dressings, where it may be
used after removal of the deposits.

The
introduction of hard mortars is one of the most common causes of failure
in historic brickwork, leading to a failure of the mortar and of the
brickwork itself.

Inappropriate
cleaning methods may cause substantial damage by removing not only
the dirt but also the fireskin, leaving a pitted face. Rotary carborundum
heads again, destroy the surface as well as dishing and scouring the 'arrises'.
Such methods may actually accelerate re-soiling and rate of decay by producing
a more textured surface.

Vegetation although often attractive, is generally harmful to older brick walls of
traditional construction. Many types of ivy can cause serious damage to
brickwork particularly if it is in poor repair, or constructed of soft,
possibly spalling, bricks bedded in soft lime mortar where the pointing
is defective.

If
not carefully removed, ivy should at the least, be heavily controlled
and never allowed to reach eaves level where it might block gutters and
downpipes. In a strong wind, vegetation can also transfer additional wind-load,
pulling out guttering, parapets, and even a chimney-stack.

Pigeons can also present problems, especially in city centres. Not only can they
force up loose roof coverings, but they will block up gutters and downpipes
with feathers, detritus and excrement, causing water penetration and consequent
decay. The faeces rapidly deface the external (as well as internal) fabric,
and may damage porous brickwork. Removal is difficult and expensive.

Control
is therefore imperative, and can involve bird nets, repellent gels, poisons,
traps and even shooting.